An oligosorbent-based aptamer affinity column for selective extraction of aflatoxin B<Subscript>2</Subscript> prior to HPLC with fluorometric detection

The article describes an aptamer affinity column for selective solid-phase extraction of aflatoxin B₂ (AFB₂). Amino-modified aptamer against AFB₂ was immobilized on CNBr-activated Sepharose through a covalent bond. The effects of oligosorbents based on 3′- or 5′-amino-modified sequences with a C6 or a C7 spacer arm were evaluated by UV spectroscopy at 260 nm. The extraction recovery was evaluated by HPLC with fluorometric detection. The extraction of AFB₂ was optimized. Under the optimum conditions, the aptamer affinity column has a linear response to AFB₂ in the range of 0.5–80 ng, with a capacity of 84.6 ng. Control supports without immobilized aptamers and a nonspecific oligosorbent immobilized with a negative control oligonucleotide were studied in order to demonstrate selectivity. The method was tested with spiked peanut sample (0.5–50 μg·kg^?1 AFB₂) and gave average recoveries of 80.9% and a mean relative standard deviation of 1.9%. The limit of detection is 25 pg·mL^?1. This is much lower than the maximum residue limits suggested by the European Union. The columns can be re-used up to five times without any loss of performance. The oligosorbent was also applied to clean-up of AFB₂ from peanut sample extracts before HPLC analysis. Results were further confirmed by ultra-fast liquid chromatography with tandem mass spectrometry. Conceivably, the method may also be applied to other samples, such as food, agricultural products, and traditional Chinese medicines.

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Graphical abstract Schematic illustration of the fabrication procedures of aptamer affinity column, AAC (a), its principle of aptamer bound to aflatoxin B₂ (b) and the obtained AAC (c).

     

Synthesis of nanocrystals via microreaction with temperature gradient: towards separation of nucleation and growth

By utilizing the symmetrical temperature distribution in a tube furnace chamber, a capillary microreactor was designed with the microchannel passing two well-controlled, stable temperatures in steep temperature gradients. The two-temperature microreator, first developed and implemented by this research team, provides an opportunity to separate the nucleation and growth of semiconductor nanocrystals, leading to better control of nucleation and growth kinetics. For the synthesis of CdSe nanocrystals as a model system, we demonstrated the improved size uniformity achieved by the two-temperature approach, confirming the success of the use of high temperature to burst nucleation and low temperature to promote growth.     

Simultaneous determination of four alkaloids in Lindera aggregata by ultra-high-pressure liquid chromatography-tandem mass spectrometry

A new separation and quantification method using liquid chromatography under ultra-high-pressure in combination with tandem mass spectrometry (MS/MS) was developed for simultaneous determination of four alkaloids in Lindera aggregata. The analysis was performed on an Acquity UPLC BEH C(18) column (50mmx2.1mm, 1.7microm particle size; Waters, Milford, MA, USA) utilizing a gradient elution profile and a mobile phase consisting of (A) water containing 10mM ammonium acetate adjusted to pH 3 with acetic acid and (B) acetonitrile. An electrospray ionization (ESI)-tandem interface in the positive mode was employed prior to mass spectrometric detection. The calibration curve was linear over the range of 17.1-856ng for boldine, 42.4-2652ng for norboldine, 6.1-304ng for reticuline and 0.5-50ng for linderegatine, respectively. The average recoveries ranged from 99.2 to 101.4% with RSDs< or =2.7%. Then, four L. aggregata samples from different batches were analyzed using the established method. The results indicated that ultra-high-pressure liquid chromatography-tandem mass spectrometry provided improved chromatographic parameters resulting in significantly increased sample throughput including lower solvent consumption and lower limits of quantitation (LOQs) for most of target analytes compared to previous method employing conventional high-performance liquid chromatography (HPLC) separation. So, the established method was validated, sensitive and reliable for the determination of four alkaloids in L. aggregata.     

Thermally-Induced Isomerization of Prenucleation Clusters During the Prenucleation Stage of CdTe Quantum Dots

The evolution of prenucleation clusters in the prenucleation stage of colloidal semiconductor quantum dots (QDs) has remained unexplored. With CdTe as a model system, we show that substances form and isomerize prior to the nucleation and growth of QDs. Called precursor compounds (PCs), the prenucleation clusters are relatively optically transparent and can transform to absorbing magic-size clusters (MSCs). When a prenucleation-stage sample at 25, 45, or 80 °C is dispersed in a mixture of cyclohexane (CH) and octylamine (OTA) at room temperature, either MSC-371, MSC-417, or MSC-448 evolves with absorption peaking at 371, 417, or 448 nm, respectively. We propose that PC-371 forms at 25 °C, and isomerizes to PC-417 at 45 °C and to PC-448 at 80 °C. The PCs and MSCs are quasi isomers. Relatively large and small amounts of OTA favor PC-371 and PC-448 in dispersion, respectively. The present findings suggest the existence of PC-to-PC isomerization in the QD prenucleation stage.     

An Unlocked Two-Dimensional Conductive Zn-MOF on Polymeric Carbon Nitride for Photocatalytic H2O2 Production

Developing highly efficient catalytic sites for O₂ reduction to H₂O₂, while ensuring the fast injection of energetic electrons into these sites, is crucial for artificial H₂O₂ photosynthesis but remains challenging. Herein, we report a strongly coupled hybrid photocatalyst comprising polymeric carbon nitride (CN) and a two-dimensional conductive Zn-containing metal–organic framework (Zn-MOF) (denoted as CN/Zn-MOF(lc)/400; lc, low crystallinity; 400, annealing temperature in °C), in which the catalytic capability of Zn-MOF(lc) for H₂O₂ production is unlocked by the annealing-induced effects. As revealed by experimental and theoretical calculation results, the Zn sites coordinated to four O (Zn-O₄) in Zn-MOF(lc) are thermally activated to a relatively electron-rich state due to the annealing-induced local structure shrinkage, which favors the formation of a key *OOH intermediate of 2e⁻ O₂ reduction on these sites. Moreover, the annealing treatment facilitates the photoelectron migration from the CN photocatalyst to the Zn-MOF(lc) catalytic unit. As a result, the optimized catalyst exhibits dramatically enhanced H₂O₂ production activity and excellent stability under visible light irradiation.     

Zincophilic Interfacial Manipulation against Dendrite Growth and Side Reactions for Stable Zn Metal Anodes

Constructing multifunctional interphases to suppress the rampant Zn dendrite growth and detrimental side reactions is crucial for Zn anodes. Herein, a phytic acid (PA)-ZnAl coordination compound is demonstrated as a versatile interphase layer to stabilize Zn anodes. The zincophilic PA-ZnAl layer can manipulate Zn²⁺ flux and promote rapid desolvation kinetics, ensuring the uniform Zn deposition with dendrite-free morphology. Moreover, the robust PA-ZnAl protective layer can effectively inhibit the hydrogen evolution reaction and formation of byproducts, further contributing to the reversible Zn plating/stripping with high Coulombic efficiency. As a result, the Zn@PA-ZnAl electrode shows a lower Zn nucleation overpotential and higher Zn²⁺ transference number compared with bare Zn. The Zn@PA-ZnAl symmetric cell exhibits a prolonged lifespan of 650 h tested at 5 mA cm⁻² and 5 mAh cm⁻². Furthermore, the assembled Zn battery full cell based on this Zn@PA-ZnAl anode also delivers decent cycling stability even under harsh conditions.     

Single-Atom Zinc Sites with Synergetic Multiple Coordination Shells for Electrochemical H2O2 Production

Precise manipulation of the coordination environment of single-atom catalysts (SACs), particularly the simultaneous engineering of multiple coordination shells, is crucial to maximize their catalytic performance but remains challenging. Herein, we present a general two-step strategy to fabricate a series of hollow carbon-based SACs featuring asymmetric Zn−N₂O₂ moieties simultaneously modulated with S atoms in higher coordination shells of Zn centers (n≥2; designated as Zn−N₂O₂−S). Systematic analyses demonstrate that the synergetic effects between the N₂O₂ species in the first coordination shell and the S atoms in higher coordination shells lead to robust discrete Zn sites with the optimal electronic structure for selective O₂ reduction to H₂O₂. Remarkably, the Zn−N₂O₂ moiety with S atoms in the second coordination shell possesses a nearly ideal Gibbs free energy for the key OOH* intermediate, which favors the formation and desorption of OOH* on Zn sites for H₂O₂ generation. Consequently, the Zn−N₂O₂−S SAC exhibits impressive electrochemical H₂O₂ production performance with high selectivity of 96 %. Even at a high current density of 80 mA cm⁻² in the flow cell, it shows a high H₂O₂ production rate of 6.924 mol g_cat⁻¹ h⁻¹ with an average Faradaic efficiency of 93.1 %, and excellent durability over 65 h.     

Prediction of quantitative calibration factors of some organic compounds in gas chromatography

A quantitative structure-property relationship (QSPR) methodology that involves multilinear (Hansch-type) and nonlinear (radial basis function neural network (RBFNN)) approaches was performed to correlate the quantitative molar calibration factors (f(M)) of 140 organic compounds against structural factors. The statistical characteristics provided by the multiple linear model (R(2) = 0.963; RMS = 0.089; AARD = 3.86% for test set) indicated satisfactory stability and predictive ability, while the predictive ability of the RBFNN model is somewhat superior (R(2) = 0.983; RMS = 0.075; AARD = 3.19% for test set). The multilinear model provided some insight into the main structure factors that modulate the quantitative calibration factor of the investigated compounds.     

Simultaneous Determination of Three Flavonoids in Rat Plasma by RP-LC After Oral Administration of the Total Flavonoids of Scutellaria barbata

A liquid chromatographic method for the simultaneous determination of three flavonoids, scutellarin (SCU), isoscutellarein-8-O-glucuronide (ISO) and luteolin (LUT) in rat plasma was developed and validated. Following a single-step liquid–liquid extraction with ethyl acetate, the analytes and internal standard (IS) (rutin) were successfully separated on a Diamonsil C₁₈ column using a mobile phase composed of acetonitrile (A)–0.2% phosphoric acid aqueous solution (B) (0–5 min, 20% A–29% A; 5–25 min, 29% A, v/v) at a flow rate of 1.0 mL min^?1. The linear range was 0.044–2.20 μg mL^?1 for SCU, 0.042–2.08 μg mL^?1 for ISO, and 0.056–2.80 μg mL^?1 for LUT, with the correlation coefficients of 0.9995, 0.9989 and 0.9963, respectively. The limit of quantification of SCU, ISO and LUT were 44, 41.6 and 56 ng mL^?1, respectively. The accuracy of assay was between 88.4 and 103.0%. The inter-day and intra-day precisions (RSD) were less than 10.5%. The developed method was simple, rapid and applied successfully to study the pharmacokinetics of SCU, ISO and LUT after oral administration of the total flavonoids of Scutellaria barbata.     

The effect of methyl group on the cooperativity between three types of hydrogen bond: O?H···O,C?H···O,and O?H···π

The effect of the methyl group on the cooperativity between three types of hydrogen bond (O H···O, C H···O, and O H···π) in cyclic complex involving an acetylene and two waters has been studied on the basis of high-level ab initio calculations. The total interaction energy of three hydrogen bonds increases as the number of methyl group in the complex increases. The binding distances of O H···π and O H···O hydrogen bonds shorten, while that of C H···O hydrogen bond elongates with increasing methyl group. This indicates that addition of methyl group leads to enhancement of O H···π and O H···O hydrogen bonds, and weakening of C H···O hydrogen bond, as also shown in frequency shift, chemical shifts, charge populations, and stabilization energies of orbital interactions. Although the presence of methyl group has a complicated effect on different type of hydrogen bond, the cooperativity of three hydrogen bonds increases in general with the addition of methyl group. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008